function check(){
	var username = $("#username"),
	    password = $("#password"),
	    userVal = username.val(),
	    passVal = password.val();
	if(userVal == null || userVal == ""){
		alert("用户名不能为空!");
		username.css("border","1px solid red");
		username.focus();
		return false;
	}else{
		username.css("border","none");
	}
	if(passVal == null || passVal == ""){
		alert("密码不能为空!");
		password.css("border","1px solid red");
		password.focus();
		return false;
	}else{
		password.css("border","none");
	}
}